WO 2004/070835 A1 discloses a method for producing microsystems comprising microelectronic components that are inserted into cavities created during the layered construction of a base body consisting of a photocurable material, said components being situated adjacent to and/or above one another on several planes and being interconnected either electrically or thermally. Once said microelectronic components have been inserted, the layered construction of the base body continues and a structure is constructed consisting of an electrically or thermally conductive material that projects vertically above the contacts (pads) of the electronic component, said conductive material producing a direct connection to an additional electronic component above the first electronic component or to one or several additional electronic components that is or are located at a lateral distance from said first component by means of a conductor track that runs horizontally from the conductive material projecting vertically above the pad. Such a method is also known as RMPD (Rapid Micro Product development) method.
These and other known methods for manufacturing a package for embedding one or more electronic components, in particular microwave integrated circuits and discrete passive components, and methods for manufacturing electronic systems show various problems or disadvantages.
The size of MMICs (Monolithically Microwave Integrated Circuits) at mm-wave/THz frequencies is often larger than half the free space wavelength λ0. This is certainly true when multiple system functions are integrated on a single MMIC. At THz frequencies chip-to-chip connections become very lossy and single-chip analog front-ends or multi-channel chips will likely be encountered with sizes larger than λ0. At chip interconnections guided wave modes get disturbed. In these regions modal coupling to unwanted cavity modes inside the package can be excited. The same modal coupling mechanisms can occur in unshielded filter sections. The package gets prone to such coupling effects when the cavities get larger than λ/2 where λ is the free space wavelength divided by the square root of the dielectric constant of the package material. Largest cavity sizes are possible using air cavities.
Dielectric losses of packaging materials increase with frequency. Thus, the full embedding of MMICs in dielectric material is practically not attractive anymore at mm-wave/THz frequencies but is done at lower frequencies. In addition, MMICs also change their behavior due to the change in the propagation constants in such an approach.
The most rigorous way to suppress cavity modes inside the package is to reduce the size of the cavities below the critical size of λ/2 where λ is the wavelength in the dielectric material (λ≦λ0). This requires the attachment of a lid on the MMIC. The photolithographically structured features on the front side of the MMIC become very small and little area is available for lid attachment on the chip. Specific processes are necessary to attach and connect a lid onto a MMIC. MMICs are often thin and fragile, and mechanical attachment to the lid is difficult, e.g. using a flip-chip approach. An alternative solution may be using lids that do not touch the MMIC but employ periodic bandgap structures. They are often difficult to design and their ability to suppress cavity modes is band-limited. In addition small manufacturing changes may shift the suppression band. Packaging of wideband systems is challenging. Alternatively, wideband absorbing materials can be introduced but they also absorb energy of information carrying guided modes.
Filter structures are required in most of receiving or transmitting mm-wave/THz systems. Their size is large compared to the wavelength and integration of such components into the package may either alter the original filter characteristic or disturb other functional blocks of the system due to modal coupling into spurious package modes.
Current low volume package solutions are composed of several different parts that need to be assembled together. Assembly and machining tolerances are critical. Achieving hermetic or near-hermetic sealing requires specialized attachment methods. On the other hand a simple package structure is required with as little manual or semi-automated assembly steps as possible. In addition, batch processing is a fundamental requirement for low-cost production.
Many packaging approaches at mm-wave and THz frequencies cannot be decomposed into electromagnetically separated units. Multichip packages are difficult to design and hard to debug due to the complex electromagnetic situation inside the package. This leads to long design cycles. Alternatively each functional block requires a separate package which leads to the problem of interconnecting these packages at mm-wave/THz frequencies. The so called split block technology is commonly in use in these scenarios which may lead to bulky and expensive electronic systems.
It shall be noted that herein reference is made to the frequency range of 30-300 GHz as mm-wave frequency range. THz frequencies and THz applications often refer falsely to a spectrum starting from 300 GHz in literature. This commonly accepted definition is adopted hereinafter, although the spectrum should actually be called the Sub-THz frequency range. Thus, references made to THz frequencies hereinafter shall be understood as comprising a frequency range from at least 300 GHz to 3 THz. Hereinafter, reference is also made to microwave frequencies, which shall be understood as the same frequency range of approximately 30 GHz to 3 THz. Microwave integrated circuits may operate up to at least 3 THz.